Along with the recent demand for miniaturization of personal digital assistances, storage devices, and the like, there has been an increasing demand for mounting of a plurality of semiconductor chips with high density. Under such circumstances, a structure having a plurality of semiconductor chips stacked therein has been studied. For example, a semiconductor module is manufactured in such a manner that an operational test is performed on each semiconductor chip in the state of a semiconductor wafer so as to select non-defective chips, and the non-defective chips are stacked. Typically, each chip has a through via hole, connecting pads formed on the top surface of the chip, and connecting bumps formed on the bottom surface of the chip. The bumps formed on an upper chip are connected to the pads formed on a lower chip, thereby electrically connecting the upper and lower chips.
However, the use of bumps to connect semiconductor chips results in an increase in connection pitch. Additionally, it is necessary to ensure a certain thickness of each chip for handling the connection between bumps and pads. These circumstances hinder a reduction in the thickness of the semiconductor module. Furthermore, an increase in the number of stacked chips may cause deterioration in the throughput of the stacking process and in the connection yield.
On the other hand, there is another method of manufacturing a semiconductor module in which semiconductor wafers are joined together and are then divided into chips. In this method, bumps for providing electrical connection between wafers can be omitted. This results in solving the above-mentioned problems which may be caused when bumps are used.
When the method of dividing the joined semiconductor wafers into chips is employed, it is impossible to select only non-defective semiconductor chips to be stacked. Accordingly, the method requires a countermeasure for avoiding the situation in which a failure occurs in the entire semiconductor module when a defective semiconductor chip is present. The situation in which a failure occurs in the entire semiconductor module can be avoided in the following manner, for example. That is, a trimming region is formed in advance for each of wiring lines connected to a via land, and if a defective chip is found, a laser beam is applied to the trimming region to disconnect the corresponding wiring line.
However, an increase in the number of disconnected wiring lines leads to an increase in the trimming region. This may result in limitation of the degree of freedom of design and deterioration in the throughput. Additionally, other problems such as a cutting failure due to insufficient welding of wiring lines, a short-circuit failure due to scattering of a metal material of wiring lines, and a lack of cutting stability due to difficulty in controlling the shape of a cut portion may occur. Especially in the case of using a copper wiring line, the difficulty in welding and cutting increases, which makes these problems more significant.
To join semiconductor wafers together, an effective structure or manufacturing process for ensuring electrical connection between via holes that penetrate wafers and semiconductor elements formed on each wafer and for ensuring electrical connection with external parts has not been established yet.